Metallic foils and particularly copper foil are used in the production of printed circuit boards. Such foils are bonded by heat and pressure to dielectric base materials, e.g. in accordance with the teachings of U.S. Pat. No. 3,328,275. The most common base material is epoxy impregnated glass fabric. In order to obtain a useful level of adherence between the copper foil and the epoxy various so-called treatments have been developed which provide the copper with a roughened surface into which the resin is forced during laminating. This roughened surface thereby provides a physical interlock between the two components. Typical treatments are described in U.S. Pat. Nos. 3,857,681, 3,293,109, and 3,918,926.
Such treatments provide a surface of the original foil with an electrodeposited metallic structure comprising copper, copper oxide, and zinc or brass. To control these sequentially deposited layers the use of grain refining agents has also been proposed, and the use of arsenic, tellurium, antimony, and other metals has been proposed as essential to the production of such treatment layers. It will be evident that the control of these layers is difficult because of their complexity and therefore adds significantly to the production cost of copper foil. It is furthermore the case that, in spite of the best efforts of the industry, variations still occur in the performance of the applied layers both in terms of copper particles residual in the base laminate after etching (called treatment transfer) and inconsistency of peel strength (the force required to strip the copper from the base material). However, more important than this is the fact that this complex metal layer, not being pure copper, interferes with the electric current carrying capability of the copper circuit tracks because a significant part of the track is of lower electrical conductivity than pure copper. Whilst these factors are manageable within the copper foil and PCB industry, increasing sophistication of circuit designs highlights the problem caused by the present technology. Therefore, a primary object of the present invention is an advantageous alternative method of promoting adhesion between metallic foils and the base material where adhesion does not rely on a substantial treatment layer of non-copper metal.